The present invention relates to the improvement of a heat fused refractory product containing zirconia. More particularly, it relates to a refractory product having higher corrosion resistance.
The heat fused refractory products are different from the burned or unburned bonded refractory products in structure and in the manufacture thereof, and have been known as high quality refractory products which have excellent corrosion resistance, abrasion resistance and compressive strength. The heat fused refractory products are cast refractory products obtained by heat-fusing desired refractory materials by an electric furnace, pouring the fused composition into a mold and resolidifying it while annealing it.
Sometimes, the fused composition is annealed in an electric furnace to resolidify it.
The present invention will be illustrated by the former embodiment. The ZrO.sub.2 -Al.sub.2 O.sub.3 -SiO.sub.2 type fused-cast refractory products containing a ZrO.sub.2 component have been widely used because the products are especially useful as the glass furnace materials.
The conventional ZrO.sub.2 -Al.sub.2 O.sub.3 -SiO.sub.2 type refractory products usually had ZrO.sub.2 contents of 30 to 35 wt.% and a maximum of about 41 wt.%.
The conditions for operating molten glass vessels and furnaces have been severe whereby higher resistances of the refractory products used in the operation have been required.
The refractory products containing higher contents of ZrO.sub.2 have been expected to provide refractory products having higher corrosion resistance. Even though such a demand exists found, a heat fused-cast refractory product containing high content of ZrO.sub.2 has not been attained because such a ZrO.sub.2 component causes significant expansion and contraction due to modifications caused by the monoclinic system .revreaction. tetragonal system transition at about 1000 .degree. C. to 1100.degree. C.
On the other hand cast refractory products having high contents of ZrO.sub.2 such as 40 to 55 wt.% of ZrO.sub.2 content have been proposed. Some products have been used in some applications.
However, in order to prevent said abnormal expansion and contraction of the product without deterioration of the corrosion resistance of the product having high ZrO.sub.2 content, the components for forming a matrix should be quite limited. The product having more than 43 wt.% of ZrO.sub.2 content has scarcely rarely been used.
On the other hand, it has been known to add CaO, MgO or Y.sub.2 O.sub.3 as a method of decreasing the abnormal expansion and contraction of ZrO.sub.2 component, that is, a method of stabilizing the ZrO.sub.2 component.
However, the method has not been effective for the heat fused refractory products.
The inventors have succeeded to provide a heat fused-cast refractory product wherein the abnormal expansion and contraction of ZrO.sub.2 component can be inhibited though the ZrO.sub.2 content is high and high corrosion resistance is imparted it is capable of being used in severe conditons though the ZrO.sub.2 content is in the conventional range.